The advent of the digital computer created a demand for direct-access storage devices capable of storing and retrieving large volumes of data. Main memory (historically referred to as "core memory" but now typically formed as semiconductor memory) and other fast electronic storage systems were not feasible for mass-storage applications primarily because of their costs, while paper, tape and floppy disk memories proved ineffective due to their Slow access times. Accordingly, digital storage devices using rotating, rigid magnetic media ("disk drives") were developed as an effective compromise between reasonable information access times and cost-effective storage capabilities. These disk drives also provided greater storage capacities for a given enclosure volume than most competing storage devices.
Disk drives typically contain one or more rotating rigid disks which have thin magnetic layers on their planar surfaces. Information is normally stored on and retrieved from the magnetic layers by means of a "flying head," which takes the form of an electromagnetic transducer element and an air-bearing slider. The slider positions the transducer on a pressurized air film at a relatively constant distance above the rotating disk surface. The pressurized air film is developed by loading a precisely shaped slider against a moving disk surface. A region of the air film moving with the disk surface is compressed by the slider, creating an air pressure that tends to force the slider away from the disk surface. By carefully controlling the shape and dimensions of the slider and the load force acting on the slider, the air being compressed between the slider and disk creates an upward pressure on the slider which maintains the slider in equilibrium at a reasonably stable distance away from the disk surface. Although this technique has traditionally been referred to as "flying-head" technology, the term "flying" is a misnomer, inasmuch as the head does not actually fly but instead is supported by a hydrodynamically lubricated air bearing.
In typical disk drives, a pair of heads is provided for use on opposite sides of each disk in order to increase the storage capacity per disk. These heads are typically mounted on support arms in a stacked configuration, with each support arm attached to a single high-speed actuator. The actuator is designed to move and position the heads accurately with respect to certain predetermined radial positions on a disk's surface, thereby permitting information to be recorded in discrete concentric tracks. Since the heads move in unison across the disk's surfaces, all of the heads on a common actuator are positioned to the same radius, and thus define a "cylinder" of tracks, which can permit any track in the current cylinder to be accessed within microseconds.
For low-performance disk drives, actuator positioning is performed "open loop", meaning that the actuator's position is determined by a device, such as a stepper motor, with no positional feedback from the disk. Open-loop methods limit areal density because they can only be used at relatively low track densities (which are measured in tracks per inch or "TPI"). In contrast, current high-performance disk drives utilize "closed loop" servo-positioning techniques to read and follow servo information stored on disks. This yields greater accuracy in positioning the actuator relative to the information recorded on a disk. Traditionally, in drives with three or more disks, the actuator's position is established with respect to a dedicated disk surface on which servo information is recorded, and all of the heads in the actuator stack are positioned in a cylinder relative to the position of the servo head on that dedicated disk surface. Alternatively, on drives with one or two disks, or on very high-performance drives, servo information is embedded within the data tracks, and head positioning is performed relative to the specific track of information being written or read.
Many computer operating systems now depend upon the availability of reasonably priced, high-performance mass-storage devices in order to implement practical solutions to such fundamental problems as the limited capacity of relatively expensive main memory. By swapping or paging portions of main memory selectively to and from a high-performance disk drive, the drive can be used, in effect, as an extension of main memory. This, in turn, permits the computer to operate on programs and data that exceed the size limitations of actual main memory. Graphical user interfaces and multimedia applications are creating even greater demand for improved disk drive performance and capacity.
Among the most important disk drive performance parameters are (1) formatted box storage capacity, (2) average access time to data, and (3) data transfer rate. Formatted box storage capacity, which measures storage capacity per unit of volume, has taken on increased importance because of the limited available space in desktop workstations, and because of the increased demand for portable, notebook, palmtop, and stylus-based microcomputer systems which are even more severely space-constrained. Access time is important because it plays a significant role in determining the typical time required to locate or store a particular unit of data on a disk drive. Finally, a high data transfer rate is important because a modem CPU can transfer data at a much faster rate than can a disk drive. This disparity creates a fundamental bottleneck in overall computer system performance that is a function of the data transfer rate. Accordingly, increases in CPU speed will not result in corresponding increases in overall system performance if the computer is input/output("i/o")-bound.
In an effort to overcome the disk drive i/o bottleneck and to improve disk drive performance, flying-head disk drive designs have continually been improved using the latest technology developments. Given the constraints of the available technology, a number of different design parameters may be altered to achieve an appropriate trade-off between improved performance, enhanced reliability, and reduced cost.
The major trend in the evolution of air-bearing, magnetic recording heads has been toward closer spacing between the slider and disk. This has been achieved by progressively making the disks flatter and smoother, by changing the shape and dimensions of the air-bearing interface, by miniaturizing the slider, and by making appropriate changes in the flexure which applies the load to the air bearing. A smaller head/disk spacing, or "flying height", increases head/disk efficiency and allows for increased areal recording density. Additionally, other disk drive performance parameters can be enhanced at lower flying heights, since the resulting improved linear and track densities permit a given quantity of data to be stored or retrieved with fewer disk rotations and with fewer, shorter head seeks.
Although lower flying heights can improve performance, they can also create a number of potential difficulties because of the fact that the resultant drives are more susceptible to problems caused by contaminants, by handling damage, by outgassing, and by other effects that produce small particles or surface irregularities. Imperfections that might not be significant at large flying heights can pose serious reliability problems at smaller head/disk spacings. Even with flatter disks having better surface finishes, the risk of high-velocity head contact with the moving disk surface, which can damage either or both components, is increased at reduced flying heights.
Notwithstanding head/disk contact during drive operation, reliable long-term drive operation can still be affected adversely by head/disk interface problems because most sliders typically "land on" a disk when the spindle motor is turned off, and "take-off" from the disk when it is restarted. This take-off and landing of sliders on smooth disks can cause stiction-related problems, abrasive wear, and head crash. In designs utilizing slider load/unload mechanisms, contact-start-stop-induced stiction and wear problems can be reduced, but such mechanisms increase costs and create additional problems in guaranteeing reliable head loading.
While flying-head designs have achieved a high degree of reliability by avoiding head/disk contact during drive operation, all known flying-head disk drive designs share certain fundamental limitations. For example, air-bearing suspensions inevitably reduce head/disk magnetic efficiency due to spacing losses. Also, because of the requisite air-bearing structure, flying heads are normally large and massive in comparison with the size and mass of the actual recording transducer. Large head size and mass limit disk-to-disk spacing, and exacerbate the problems that arise when a head structure contacts a disk surface. A large slider mass also requires the use of far more powerful actuators, particularly in high-performance drives having multiple heads and disks, than would be required, for example, to move and position the transducer masses alone.
Considering further issues, the changes in the local surface velocity of a disk at different radii thereon creates additional problems for flying-head drives, since both flying height and air-bearing stiffness change in response to changes in air-film speed. In disk drives utilizing rotary actuators, head skewing causes changes in the air-pressure profiles along the air-bearing surface, which changes can cause similar difficulties. Finally, prior art flying-head, contact-start-stop drives are subject to stiction. They therefore require high-torque motors to ensure that disk rotation can be initiated despite stiction and friction arising from head/disk contact prior to head take-off. The resultant increase in power consumption can be especially detrimental in portable, notebook, palmtop, and stylus-based computer disk drive applications due to the power limitations imposed by the use of batteries in these products. Higher power consumption also increases heat generation, which can adversely affect the reliability of the drive system.
Significant advances over prior art flying-head technology have been disclosed in the following U.S. patents and co-pending U.S. patent applications: U.S. Pat. No. 5,041,932 for INTEGRATED MAGNETIC READ/WRITE HEAD/FLEXURE/CONDUCTOR STRUCTURE, issued Aug. 20, 1991, U.S. Pat. No. 5,073,242 for METHOD OF MAKING INTEGRATED MAGNETIC READ/WRITE HEAD/FLEXURE/CONDUCTOR STRUCTURE, issued Dec. 17, 1991, U.S. Pat. No. 5,111,351, for INTEGRATED MAGNETIC READ/WRITE HEAD/FLEXURE/CONDUCTOR STRUCTURE, issued May 5, 1992, U.S. Pat. No. 5,163,218, for INTEGRATED MAGNETIC READ/WRITE HEAD/FLEXURE/CONDUCTOR STRUCTURE, issued Nov. 17, 1992; U.S. patent application Ser. No. 07/684,025 for WEAR-RESISTANT HEAD FOR CONTACT READING AND WRITING MAGNETIC MEDIA, filed Apr. 10, 1991; U.S. patent application Ser. No. 07/746,916 for UNITARY MICRO-FLEXURE STRUCTURE AND METHOD OF MAKING SAME, filed Aug. 19, 1991; and U.S. patent application Ser. No. 07/760,586 for HIGH-CAPACITY, MICRO-SIZE, RIGID-DISK, MAGNETIC DIGITAL-INFORMATION STORAGE SYSTEM, filed Sep. 16, 1991; and U.S. patent application Ser. No. 07/783,619 for GIMBALED MICRO-HEAD/FLEXURE/CONDUCTOR ASSEMBLY AND SYSTEM, filed Oct. 28, 1991. The respective disclosures of these documents are hereby incorporated by reference into the present disclosure.
Taken together, and more particularly, with various ones of their respective innovative features "gathered" into one selected operative whole, the inventions illustrated and described in the just-cited materials reveal extremely low-mass, integrated (and gimbaled) head/flexure/conductor structures wherein the head and flexure combination yields an extremely small, low-mass unit, and wherein further, the conventional "flying" slider has been replaced by a contact-capable structure featuring a hardened wear pad with greatly miniaturized dimensions. This wear pad is disposed immediately adjacent a head/transducer, with which it is formed on a minute ceramic structure which, in the integrated form referred to above, forms an end portion of an elongate flexible ceramic cantilevered beam, and which, in the gimbaled form referred to above, is joined to the free end of such a beam for articulation relative thereto through gimbal structure. In both the integrated and the gimbaled organizations, the beam effectively supports and loads the pad against, and for substantially continuous, microscopic-area contact with, a moving recording-surface medium, thus to place the pole portion of the transducer in extremely close proximity to the recording surface. Formed in the ceramic structure, as will be explained below, are the other magnetic components that make up the balance of the magnetic portion of the transducer (which can take any one of a variety of magnetic forms), as well as associated conductive windings, and conductive traces which extend from the free, distal, working end of the head/flexure/conductor structure toward the opposite end for suitable signal-communication connection with the appropriate world "outside of" the beam/flexure/head/transducer organization.
Included in several of the drawing figures herein, and discussed and described below, are several greatly enlarged views illustrating some of the key features of several embodiments of head/flexure/conductor structures which have been selected for illustration in the preferred form(s) of the invention herein disclosed. Further details of these structures, of related others, and of the process(es) for manufacturing the same, are found inter alia, in the elaborated disclosures in the patent and patent applications referred to above and incorporated herein as an integral part of the disclosure in this specification. Also incorporated by reference into this text to highlight the versatility of the invention vis-a-vis employing various head (transducer) structures, are U.S. Pat. No. 4,751,598 (cross-field transducer), U.S. Pat. Nos. 4,878,140, 5,073,836 (magneto-resistive transducers), and as a prior art background publication a book by C. Denis Mee and Eric D. Daniel entitled "Magnetic Recording Handbook", .COPYRGT.1990 by McGraw-Hill, Inc. The term "head structure" employed herein throughout embraces this wide range of magnetic transducer modalities.
The significant reductions in head/flexure/conductor size, effective mass, and required load which are offered by the highly miniaturized, integrated and gimbaled structures now being referred to readily permit the media-contacting wear pad (referred to above) to be operated confidently in sliding contact with a recording surface in a rigid disk, essentially for the lifetime of the associated disk drive system, without any appreciable risk of physical damage to either component. Contact "magnetic coupling" of these two elements strikingly reduces the kinds of "spacing" losses that characterize prior art "flying" disk drive system technology, and greatly improves the electromagnetic signal-transmission efficiency of the resulting head/media interface system with startling improvements in information-storage areal density. It is the combination of this low-mass, miniature-size, sliding-contact organization within the overall system that offers the novel head/disk interface advantage referred to above, and that forms a core contribution in the system of the present invention.
From the statements given just above regarding various conditions found in prior art "flying-technology" disk drive systems, and from the significant improvement opportunities that are offered by features of the inventions described and illustrated in the above-referenced issued patent and co-pending patent applications, one can state that an important general object of the present invention is to provide a reliable, high-performance, rigid disk drive system for storing and reproducing digital information, which system is characterized by highly efficient data transfer, by a large storage capacity per unit of volume, and by a greatly improved read/write head/disk interface region which contributes significantly to such "capacity/efficiency" advances.
Another and related object of the invention is to provide such a system in which high performance and large capacity per unit of volume advances are achieved through employing contact reading and writing, utilizing a greatly miniaturized electromagnetic read/write head structure and elongated flexure structure which collectively have an effective mass of less than about 1.5-milligrams. Both integrated and gimbaled constructions of this organization are shown and achieve this objective.
Further objects of the present invention include the provision of: a storage system wherein position control of the head structure and flexure structure is provided by a precision, low-mass servo/actuator; a storage system which has reduced power requirements; such a system which will not experience a head crash; a system which operates with significantly lighter applied head loads; a system of the type outlined which is substantially free from the effects of stiction; a system offering all of the above in conjunction with notably fast seek times; and a system which, because of the features that characterize what has been referred to herein as the improved read/write head/disk interface region, offers a greatly enhanced storage capacity per unit of volume than is offered by known prior art systems, regardless of the particular, selected media form factor.
These and other important features, objects and advantages which are attained by the present invention will become more fully apparent as the description that now follows is read in conjunction with the accompanying drawings.